Fluid heating apparatus



Sept. 7, 1954 c. B. BAVER FLUID HEATING APPARATUS Original Filed March 20, 1942 Fig.2

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CW 5. Ba 1/ Sept. 7, 1954 Original Filed March 20, 1942 c. B. BAVER 2,688,466

FLUID HEATING APPARATUS 5 Sheets-Sheet 3 226'\ s a i v l s z E i 5 g 2 a. Home M 5 236 7 g 232 \g INVENTOR.

Patented Sept. 7, 1954 FLUID HEATING APPARATUS Clyde B. Baver, Fanwood, N. J assignor to The Babcock & Wilcox Company, Rockleigh, N. J., a corporation of New Jersey Original application March 20, 1942, Serial No. 435,466, now Patent No. 2,418,815, dated April Divided and this application February 1, 1947, Serial No. 725,901

10 Claims.

The invention disclosed herein relates to fluid heating apparatus utilizing gaseous products of combustion as the heating medium, and more especially to the arrangement of heating surface in such apparatus whereby heating gases of different characteristics may be advantageously utilized to obtain effective heat transfer at relatively high efficiencies under varying conditions.

l'he invention is particularly applicable to direct-fired boiler units wherein the hot heating gases are derived from the combustion of fuel in an associa ed furnace, and wherein the total fluid heating surface is distributed between a plurality of components or sections, including for example a vapor generating component or section, together with auxiliary fiuid heating components or sections arranged for the heating of fluids of liquid or gaseous character, the heating gases being directed through such sections in a manner maintaining draft losses within predetermined limits under varying gas weight conditions, as fully set forth in Patent 2,418,815, dated April 15, 1947, as issued in my copending application Serial No. 435,466, filed March 20, 1942, of which the present application is a division.

In the usual arrangement of boiler unit it has been customary to direct the flow of heating gases from the furnace over the convection heated sections of the unit in series, and with such an arrangement adapted to operate efiiciently with a fuel having characteristics giving high weights of combustion gases per unit of heat liberation, it has been necessary to sacrifice efficiency when firing with a fuel of comparatively low gas weights since the lower mass flow seriously affects the rate of heat absorption. The alternative to this would have been to accept a compromise between the performances of the different fuels without realizing with any of the fuels the maximum efiiciency which could have been derived from operation at all times with a single type of fuel.

A specific illustration is in the case of a boiler unit fired at one time by blast furnace gas, having a low calorific value, and at another time by some other fuel such as pulverized coal, or oil, having comparatively high calorific value, where calorific value, as hereafter used for the purpose of this disclosure, is in terms of theB. t. u. liberation of the specific fuel per unit of Weight of the resultant gaseous products of combustion. In such a case, in order to provide the same output of vapor when operating with blast furnace gas as with pulverized coal or oil, the extent and arrangement of the heat transfer surface has been determined from characteristics of the fuel of lower calorific value, due to the extremely high weight of heating gas flow required for the desired maximum capacity of the unit, and the consequent high draft loss through the convection heated fluid heating sections which determines their sizes and proportions. When the shift is made to a fuel of higher calorific value, the weight of the heating gases required for the same output is considerably less so that the accompanying draft loss through the unit becomes extremely low, with the proportions of the heating sections fixed, as is customary, and although the heating sections contain a generous amount of heat transfer surface, as provided by tubes or other forms of heat transfer elements, such surface is not being utilized effectively due to low gas velocities and corresponding low mass flow.

When fuels are burned with customary proportions of excess air to give proper combustion as afforded by fuel burners now in use, the weight of the gaseous products of combustion resulting from different fuels may vary widely, for a given value of heat liberation, due in part to the fact that certain fuels, particularly a gaseous fuel such as blast furnace gas, contain constituents such as nitrogen which contribute little or nothing to the calorific value of the fuels but rather reduce the ultimate temperatures of the combustion gases.

The relative heating characteristics of a selected variety of fuels commonly used are indicated by the combustion gas Weights under perfect combustion conditions for a heat liberation of 10,000 B. t. u., as follows:

Weight of combustion gases Lbs. per 10,000 B. t. u.

Blast furnace gas 15.4' Pulverized coal -i 10.2 Oil 9.2

The wide variation in heating gas weights for these same fuels, is indicated by the following specimen tabulation based on an output capacity for a particular boiler unit of about 150,000 pounds of steam per hour:

Weight of heating gases (gaseous products of It may be concluded therefore, that when blast furnace gas is burned to give the same resultant absorption in a boiler unit, the resultant products of combustion will be much higher in weight than with richer fuels such as oil or pulverized coal.

When the weight of products of combustion per unit of heat liberation is high, as for example in the case of blast furnace gas, the quantity of gas determines the characteristics of the draft apparatus such as the induced draft fan and stack. If the same furnace and heat absorbing equipment, such as a boiler and its associated fluid heating sections, is to be fired at times with a second type of fuel having characteristics such that the quantity of products of combustion per unit of heat liberation will be materially lower, as for example oil, then the draft loss Will be very materially lower as will the mass flow with reference to the tubes or heating surfaces, with lower efficiency of heat absorption resulting.

Thus, if the tube spacing and fan are selected for blast furnace gas only, the operation of the same equipment fired by oil will be uneconomical because of low rates of heat transfer to heating surface because of low mass flow. On the other hand if .the apparatus is selected for good heat absorption on the basis of the higher grade fuel such as oil, the fan would be inadequate to handle the greater quantity of gases with the lower grade fuel for generating the same quantity of steam. A large proportion of the total draft loss of a modern boiler unit results from the gas flow resistance of the convection heated fluid heating sections which are placed beyond the boiler section and act to reduce the temperature of the gases below the saturated temperature of the boiler water. Accordingly, I divide and arrange the heating surface involved in such sections, and provide for alternate gas flow paths therethrough, so that the maximum draft loss or flow resistance may be kept within predetermined limits even though the gaseous products of combustion may vary widely, as for example to the extent of from 58,000 pounds per hour when operating with a high grade fuel at a low rating of the boiler unit to 334,500 pounds per hour when operating at a high rating with a low grade fuel. With gas weights varying to the extent indicated, in a ratio of approximately 1:5.70, the corresponding variation in draft loss is in greater ratio, substantially in proportion to the squares of the Weights, and accordingly presents a serious limitation to the operation of the unit.

For an assumed maximum load condition of about 150,000 lbs/hr. the weights of the heating gases might vary from about 179,500 lbs/hr. using a high grade fuel, to about 334,500 lbs/hr. using a lower grade fuel, the weight ratio being about 1:1.80, and the resulting draft loss ratio about 1:3.50.

It is a purpose of the invention therefore to obviate such wide variations in draft resistances, and still make it possible to attain full load operation if desired at reasonably high efficiencies.

Another object of the invention is to arrange the fluid heating sections of a vapor producing unit so that the heating surfaces of such sections are utilized to best advantage over a range of varying heating gas weight conditions; for example, when fuels of different heating characteristics are used at different times to provide a given output capacity, or when the same fuel is F used continuously at varying rates to provide varying output capacities.

Another object of the invention is to provide an arrangement of apparatus for the recovery of heat from the heating gases leaving a steam boiler whereby wide variations in the total weight of such gases resulting from the burning of different fuels may be utilized With good efficiency of heat absorption and with an induced draft installation economical both from the standpoint of installation and operating cost.

Another object involves the control of heating gas flow through fluid heating sections whereby with increasing rates of heating gas flow the variations in gas flow resistance are maintained proportionately lower than the variations in heating gas weight.

An additional object is directed to the operation of convection heated fluid heating sections whereby fluid to be heated is caused to flow through the sections in series and heating gases are selectively directed so as to flow through the sections along paths of different gas flow resistances.

A more specific object pertains to the construction and operation of a vapor generating unit whereby heating gases resulting from the combustion of fuels of different calorific values are discharged from a boiler section and directed in series or in parallel through associated sections in which air is preheated for the combustion of such fuels.

A further specific object is in the provision of dampered duct means defining gas and air flow paths related to multiple sections of an air heater whereby through selective operation of associated dampers the gases may be directed through the sections in series or in parallel, or through one of the sections only.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of my invention.

Of the drawings:

Fig. 1 is a side elevation, in section, of a boiler unit illustrating an embodiment of my invention; and,

Figs. 2 and 3 are vertical and plansections respectively of apparatus shown in Fig. 1, taken along lines 2-2 and 33.

In the embodiment of my invention as herein illustrated, the boiler or vapor generating unit includes a furnace I54 arranged for the combustion of difierent fuels simultaneously or at different times, such fuels differing particularly in their relative calorific values as previously defined, ports I56 at two levels in an upright wall of the furnace being indicated for burners utilizing a fuel of relatively high calorific value such as pulverized coal or oil, for example, and ports I 58 for burners utilizing a fuel of relatively low calorific value such as gaseous fuel of the character of blast furnace gas, for example. Hot combustion air is suitably supplied to burner ports I56 through branch duct I60, and to burner ports I58 through branch ducts I62, each duct being a branch of the main hot air supply duct I64, and the supply of air through each duct being separately regulated by dampers I66 and I68, respectively. The specific forms of burners utilized in each case may be of suitable known construction, and may be of such types as indicated, for example, in Figs. 1 and 5 of the aforesaid parent application, now Patent No. 2,418,815.

The fluid heating surfaces of the illustrative boiler unit include a convection heated vapor generating section or component iIIl arranged relative to the flow of heating gases from the laterally adjacent furnace or combustion chamber I54, essentially as disclosed in U. S. Patent 1,999,984., E. G; Bailey et al., the boiler section I 79 comprising a main bank of closely spaced upright tubes i'II extending between and connected to upper and lower drums I13 and I75, the gases entering the tube bank space In from around one end of the longitudinal baffle I'M; The flow of heating gases over the tubes of the bank is maintained substantially horizontal throughout a plurality of serially connected transverse passes, including passes I76 and I18 separated by baffle I80 as indicated in part in Fig. '3; As a modification of the patented disclosure, spaced boiler tubes I82, having ends connected to the upper and lower drums I13 and I15, are arranged in a row spaced from the boiler tube bank I'll), the row of tubes I152 defining a vertically elongated gas space I84 rearwardly of the bank and providing intermediate tube length portions arranged along an upright side wall I'l'l of the setting in cooling relation thereto. The heating gases discharged from the boiler pass I'Hl enter the adjacent gas space I84 and'from there are discharged across end portions of the tubes I82 either through the upper gasoutlet I136 in the roof of the setting adjacent upper drum I13 or through the lower side wall gas outlet I88 adjacent lower drum I715. Dampers lat] and I92 are included for regulating the flow of heating gases through the respective gas outlet openings.

A tubular air heater 194 located adjacent the furnace setting comprises an outer casing I95 having upper and lower tube sheets I98 and 293 at opposite ends to which vertically disposed heating gas tubes 282 are connected, thereby providing tube sheet connections substantially in a common plane at each end, the tubes being arranged in two groups "2% and 2% longitudinally of the setting wall I". A duct 208 having its inlet over the roof outlet I85 serves as a conductor for heating gases to the space 2H] above the upper ends of both groups of air heater tubes 202 when damper Isl is in an opened position. A hopper compartment 2l2 below the air heater tubes 2532 is divided by a partition 2 M to provide a space 2H5 below the group of tubes 2% and a space 2H! below the group of tubes 2%, the partition having an opening 225? therein in which damper 222 is located.

The air heater gas outlet is provided by an opening 224 at one end of the hopper compartment M2, the spent gases being discharged through outlet opening 221i and connecting duct 226 and through the induced draft fan 228 to a stack, not shown.

Air to be heated for combustion of fuel in furnace chamber I54 is supplied to the air heater through inlet duct 2% under pressure from the forced draft fan 232,'th'e air being directed horizontally across both. groups of tubes 2412 in a single pass from inlet 23s to outlet 2% where connection is made with the main hot air supply duct I66 previously mentioned. The division of the air heater tubes 202 into two groups 204 and 2% thus provides a plurality of fluid heating sections in which the fluid to be heated, in this instance air, is directed in series therethrough. This division of the air heater surface so as to form two fluid heating sections, in conjunction with the associated dampered conduit means provided, enables the heating gases to be directed through both sections in series or in par" allel, or through one section'only, as desired, in order to maintain relatively high efficiencies of heat absorption at varying rates of heating gas flow as will presently appear.

When the boilerunit is being fired with a fuel of relatively high calorific value, such as pulvericed coal or oil, for example, the gaseous prodnets of combustion are relatively low in weight so that the entire output of heating gases may be directed through the various fluid heating sections in series with onlya nominal draft loss resulting. However, when firing with a fuel of relatively lowcalorific value, such as blast furnace gas, for example, for an equivalent normal load or output capacity, the weight of the heating gases is considerably increased; in which case, for serial flow of all gas through all sections, the resultant draft loss through both air heater sections isincreased in even greater proportion. Similar increases in draft loss may result when firing the unit at increasing rates to provide increasing output capacities, utilizing either a single fuel of a given calorific value, or a combination of fuels of different calorific values.

Thus, when the boiler unit is being fired with pulverized coal or oil, for example, under which condition heating gas weights are relatively low, the damper I99 across the roof outlet I86 may be closed, and the damper I92 across the lower outlet 83 opened, thereby causing the heating gases to be discharged across the lower ends of tubes it?! through lower outlet I88 into the coinpartment space 2I5. With the partition damper 222 closed, the gases are directed through both groups of air heater tubes 2M and 266 in series, all of the gases first flowing upwardly'throu'gh the first group of tubes 2M, turning in the space 2m above the groups, and flowing downwardly through the second group of tubes 206 into the compartment space 2H2, from whence the waste gases are discharged to the stack, as previously described.

When a fuel such as blast furnace gas is used for firing, requiring a substantially greater weight of combustion gases to flow through the unit, for a given vapor output, it is preferable to provide parallel flow throughthe two groups of air heater tubes in orderto minimize draft losses. For this condition, the upper damper I90 is opened and the lower damper I92 closed, thereby causing the heating gases tobe discharged across the upper ends of tubes I82 direct to the space 2E0 above the air heater tubes 202. The flow of gases is then divided between the groups of tubes 2% and 206, one part flowing downwardly through tubes 204 to space 2H3 and another part flowing downwardly through tubes 206 to space 2I8 in parallel with the first part; the partition damper 222 being opened to provide an outlet for gas from space 2I6- whereby the total quantity may be discharged from space 2I8, as before, through the gas outlet 224.

As a further variation in the path of heating gas flow, for conditions of relatively low heating gas weights for example, the dampers I92 and 222 -may be closed, and damper I96 opened, so that all gases aredirected through only one of the fluid heating sections, the gases being disoharged'fromthe boiler section through the upper gas outlet I36 and being directed through only the one group of air heater tubes 206. If desired, a major'portion of the heating gases may be caused to bypass both air heating sections 204 and 206 by opening the lower outlet damper I92 and the partition damper 222, and closing the upper outlet damper 199, the main body of gases then passing direct from the lower gas outlet I88 through openings 220 and 224 to the fan 228 and the remainder of the gases flowing in series through sections 204 and 206.

While in accordance with the provisions of the statutes I have illustrated and described herein one of the best forms of my invention now known to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departingfrom the spirit of the invention covered by my claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

I claim:

1. In a fluid heater having a pair of separate heating gas inlets, a pair of heat exchangers arranged at a substantially common elevation, a dampered conduit system containing said heat exchangers and terminating in conduit portions respectively connecting the aforesaid inlets to opposite ends of both said heat exchangers, one of said conduit portions providing an outlet for said gases at a location remote from the gas inlet to which said portion is connected, separate damper means directly associated with each of said gas inlets, and damper means in said one conduit portion providing said gas outlet, between corresponding ends of said heat exchangers, arranged in one operating position to provide a heating gas flow path through said pair of heat exchangers in series from one of said inlets, and in a second operating position to provide a heating gas fiow path through said pair lower ends of said flue portion and thereby to corresponding upper and lower ends of both saidv heat exchangers, said lower conduit portion having a gas outlet at one end horizontally separated from its gas inlet adjacent its opposite end, separate damper means directly associated with each of said gas inlets, and damper means in said lower conduit portion, between corresponding lower ends of said: heat exchangers, arranged in its closed operating position to provide with said fiue and said conduit portions a heating gas flow path through said pair of heat exchangers in series from said lower inlet, and in an open operating position to provide a heating gas flow path through said pair of heat exchangers in parallel from said upper inlet.

3. In a fluid heater having a pair of separate longitudinally spaced heating gas inlets arranged at opposite ends thereof, fluid heating apparatus disposed between said inlets and having a total area of heating surface arranged in substantially equal portions at opposite sides of a plane extending in the general direction in which said inlets are spaced, means for directing fluid to be heated through each of said heating surface portions, conduit means connecting said inlets and containing said heating surface portions in successive relation transversely of said plane, said conduit means terminating at opposite ends in conduit end portions each providing one of said inlets and extending to the adjacent ends of said heating surface portions, one of said conduit portions having a partition therein substantially in alignment with said plane, separate damper means in each of said inlets for controlling heating gas flow into the respective conduit end portions, and damper means in said partition arranged in its open operating position to provide a heating gas flow path from one of said inlets over said total heating surface area, and in its closed operating position to provide a heating gas flow path either from said one inlet over a heating surface area restricted to one of said portions or from the other of said inlets over said total heating surface area.

4. In a fluid heater having a separate upper and a separate lower heating gas inlet, a pair of laterally adjacent fluid heating sections each having its heating surface at one side of a given upright plane, a conduit system containing said sections and terminating at opposite ends in upper and lower duct means respectively connecting said upper and lower gas inlets respectively to upper and lower end portions of said sections, said lower duct means having a partition therein substantially in alignment with said plane, means for directing fluid to be heated through said sections in series, separate damper means directly associated with each of said inlets for controlling heating gas flow into said upper and lower duct means respectively, and damper means in said partition arranged in its open operating position to provide a heating gas flow path from said lower gas inlet through both of said sections, and in its closed operating position to provide a heating gas flow path either from said lower gas inlet through both of said sections or from said upper gas inlet through one of said sections only, each of said flow paths containing heating surface restricted to heating surface provided by said pair of fluid heating sections.

5. In an air heater having a separate upper and a separate lower heating gas inlet, a pair of horizontlly adjacent air heater sections each having its heating surface provided by a group of upright gas conducting tubes arranged at one side of a given upright plane, said air heater having vertically spaced tube sheets to which opposite ends of said tubes are connected, a conduit system containing said sections and terminating at opposite ends in upper and lower duct portions respectively connecting said upper and lower gas inlets respectively to the upper and lower ends of said groups of tubes, said lower duct portion having a partition therein and thereacross substantially in alignment with said plane, means including said tube sheets for directing air to be heated through each of said sections, separate damper means associated directly with each of said inlets for controlling heating gas flow into said upper and lower duct portions respectively, and damper means associated directly with said partition arranged in its open operating position to provide a heating gas flow path from said upper gas inlet through both of said sections in parallel, and in its closed operating position to provide a heating gas flow path either from said lower gas inlet through both of said sections in series, or from said upper gas inlet through one of said sections only.

6. In fluid heating apparatus having vertically separated heating gas outlets from which heating gases are discharged at different times, a conduit system having upper and lower conduit portions respectively providing an upper and a lower heating gas inlet arranged to receive said gases from the respective elevations at which said gases are discharged, a plurality of fluid heating sections arranged in horizontal succession within said conduit system, and dampers positioned in said conduit system and operable to provide a heating gas flow from said lower gas inlet through said fluid heating sections in series or from said upper gas inlet through said fluid heating sections in parallel, said lower conduit portion being continuously open to the lower ends of said fluid heating sections and having one of said dampers in said lower conduit portion at a position intermediate the lower ends of a pair of said fluid heating sections.

7. In fiuid heating apparatus having vertically separated heating gas outlets from which heating gases are discharged at different times, upper and lower duct means respectively providing an upreceive said gases from the respective elevations at which said gases are discharged, a plurality of serially connected fluid heating sections for heating a common fluid arranged in horizontal succession between said upper and lower duct means, a partition extending upright across said last named duct means and defining a separate gas flow space beneath each of said sections, and dampers associated respectively with each of said inlets and with said partition and operable to selectively provide a heating gas flow from said upper gas inlet through said fluid heating sections in parallel or a heating gas flow from said lower gas inlet through said fluid heating sections in series.

8. In fluid heating apparatus having vertically separated heating gas outlets from which heating gases of different calorific values are discharged at difi'erent times, a conduit system having upper and lower conduit means respectively providing an upper and a lower heating gas inlet arranged to receive said gases from the respective elevations at which said gases are discharged, an air heater withinsaid conduit system having upright gas conducting tubes in communication with said separate conduit means and arranged in horizontally successive groups, upper and lower tube sheet means to which opposite ends of said tubes are connected arranged at one end at least in a substantially common plane, each of said conduit means providing a gas flow chamber outwardly adjacent one of said tube sheet means in communication with the adjacent open end portions of all tubes of said groups, a partition in one of said chambers defining gas flow compartments each in communication with tubes of a single group, means including said upper and lower tube sheet means for directing air to be heated across the tubes of each of said groups, and damper means associated with each of said conduit means for varying the path of gas flow through said groups of tubes.

9. In fluid heating apparatus having vertically separated heating gas outlets from which heating gases of different calorific values are discharged at different times, a conduit system having separate conduit means respectively providing an upper and a lower heating gas inlet arranged to receive said gases from the respective elevations at which said gases are discharged, an air heater within said conduit system having upright gas conducting tubes in communication with said separate conduit means and arranged in horizontally successive groups, upper and lower tube sheet means to which opposite ends of said tubes are connected, each of said conduit means providing a gas flow chamber outwardly adjacent one of said tube sheet means in communication with the adjacent open end portions of all tubes of said groups, said chamber adjacent one of said tube sheet means being formed with separate compartments each in communication with tubes of a single group, means for directing air to be heated through all of said tube groups in series, and damper means positioned in said conduit system and operable to selectively provide heating gas flow paths of different gas flow resistances through all tubes of said groups.

10. In fluid heating apparatus, the structure as defined in claim 9 wherein said gas flow chamber is positioned subjacent said lower tube sheet means and a partition within said chamber defines said gas flow compartments, said damper means including a separate portion operably associated with said partition.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,378,348 Hartwell May 17, 1921 1,768,056 Hartmann June 24, 1930 2,131,058 Lucke Sept. 27, 1938 2,213,324 Niemitz Sept. 3, 1940 2,386,188 Artsay Oct. 9, 1945 2,392,325 Kuhner Jan. 8, 1946 FOREIGN PATENTS Number Country Date 151,614 Great Britain Oct. 27, 1921 234,923 Great Britain June 11, 1925 539,615 Great Britain Sept. 17, 1941 505,307 Germany Aug. 18, 1930 526,173 Germany June 3, 1931 

